The maintenance of power tools and power cables in a proper and safe operating condition is a problem to which considerable attention need be given. In particular, electrically powered tools and cables used at construction sites must be tested for proper wiring conditions periodically so as to comply with governmental safety regulations as well as to insure their proper operating condition. In order to determine the proper and safe operating condition of a power tool or power extension cable, it is necessary to perform a number of individual tests. Due to the large number of tools and cables which may be utilized at a construction site, it is necessary that the individual tests be performed as expediently as possible without sacrificing any quality and reliability in the testing procedures.
Prior devices have been developed for testing the electrical circuits of power tools such as those disclosed in U.S. Pat. Nos. 3,878,458, 3,368,146 and 3,141,128. These devices include various circuit arrangements for testing electrical power tools for a defective ground circuit and for determining whether the frame of the power tool is properly grounded. In addition, U.S. Pat. No. 3,368,146 discloses a test for checking the wiring condition of a three-wire extension cord. However, this test requires that the testing device be unplugged from the AC wall receptacle and the extension connected between the wall receptacle and the testing device. These devices include rather complicated testing circuits and switching circuits to control the various tests being performed which increase the difficulty of operation and adversely affect the reliability of the tests.